Cecil Moore wrote:

Craig Buck wrote:

I was talking about radiation efficiency taking into account the ground
losses. The ARRL Antenna Book equation is Efficiency = Radiation
Resistance
divided by the sum of Radiation Resistance + Ground loss + Coil loss.
Plug
in a 6 ohm ground loss and whatever you want to assume for the coil loss.
The higher the radiation resistance the higher the efficiency. No?


For an 8 ft center-loaded whip on 75m, the ARRL Antenna Book gives 0.8 ohms
as the radiation resistance and 22 ohms as the feedpoint impedance. That's
an efficiency of about 3.6%, about 4 watts radiated for 100 watts input.

Keeping Ground Loss and Coil Loss constant and increasing the radiation
resistance from 0.8 ohms to 1.6 ohms changes the efficiency to 7%. Hmmm
.... the higher the radiation resistance the higher the efficiency!!

"Dave Shrader" wrote in message
news:hBdPb.92880$nt4.225549@attbi_s51...
Cecil Moore wrote:

Craig Buck wrote:

I was talking about radiation efficiency taking into account the ground
losses. The ARRL Antenna Book equation is Efficiency = Radiation
Resistance
divided by the sum of Radiation Resistance + Ground loss + Coil loss.
Plug
in a 6 ohm ground loss and whatever you want to assume for the coil
loss.
The higher the radiation resistance the higher the efficiency. No?


For an 8 ft center-loaded whip on 75m, the ARRL Antenna Book gives 0.8
ohms
as the radiation resistance and 22 ohms as the feedpoint impedance.
That's
an efficiency of about 3.6%, about 4 watts radiated for 100 watts input.

Keeping Ground Loss and Coil Loss constant and increasing the radiation
resistance from 0.8 ohms to 1.6 ohms changes the efficiency to 7%. Hmmm
... the higher the radiation resistance the higher the efficiency!!

In all the cases I reported the antennas were on the same ball on the same
truck: ground losses were a constant.
They were all of comparable length, the Hustler a bit shorter than the
screwdriver, the bugcatcher a bit longer, but comparable radiation
resistances; about an ohm.
The lower the loss resistance the higher the efficiency, which gets back to
the ~10 ohms of the screwdriver;
Comparing that to the ~20 ohms of the Hustler and bugcatcher leads me to
suspect the difference is in the loss resistance which is consistent with
observed performance on the air.
With my 200 watt mobile rig I should radiate about 16 watts on 80!
;^)
73
H.
NQ5H

H. Adam Stevens, NQ5H wrote:
Comparing that to the ~20 ohms of the Hustler and bugcatcher leads me to
suspect the difference is in the loss resistance which is consistent with
observed performance on the air.

There's something wrong with the bugcatcher feedpoint impedance
unless there was a matching coil, cap, or transformer at the base.
Did you have any coils shorted out on the loading coil for tuning
purposes? Shorted coils lower the Q.
--
73, Cecil http://www.qsl.net/w5dxp



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Mark Keith wrote:

"H. Adam Stevens, NQ5H" wrote:
band Hustler Screwdriver 103"/BugCatcher/54"
80 21 ohms 9 ohms 23 ohms
I really thought the huge bug catcher would do better.

I'm not sure if I'm getting the problem. Is the bugcatcher failing to
perform?

With that much whip and base section, the bugcatcher coil probably
had shorted turns to raise the resonant frequency. It is well known
that shorted turns on a high-Q coil lowers the Q. (Try a shorted turn
on an iron core choke.)
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Mark Keith wrote:

"H. Adam Stevens, NQ5H" wrote:
band Hustler Screwdriver 103"/BugCatcher/54"
80 21 ohms 9 ohms 23 ohms
I really thought the huge bug catcher would do better.

I'm not sure if I'm getting the problem. Is the bugcatcher failing to
perform?

With that much whip and base section, the bugcatcher coil probably
had shorted turns to raise the resonant frequency. It is well known
that shorted turns on a high-Q coil lowers the Q. (Try a shorted turn
on an iron core choke.)
--
73, Cecil http://www.qsl.net/w5dxp


Nope, the whole coil, I just found the resonance and noted the value of R.
73
H.
NQ5H

"Cecil Moore" wrote in message
...
H. Adam Stevens, NQ5H wrote:
Comparing that to the ~20 ohms of the Hustler and bugcatcher leads me to
suspect the difference is in the loss resistance which is consistent
with
observed performance on the air.

There's something wrong with the bugcatcher feedpoint impedance
unless there was a matching coil, cap, or transformer at the base.
Did you have any coils shorted out on the loading coil for tuning
purposes? Shorted coils lower the Q.
--
73, Cecil http://www.qsl.net/w5dxp



Nope
Just the Hustler base, the entire bugcatcher coil and a 103 " whip.
I expected it to be lower in impedance at resonance.
Now I've ordered a BBS screwdriver to see if the copper base is better than
aluminum.
Copper has about a tenth the resistance of aluminum, we shall see.
H.
NQ5H

H. Adam Stevens, NQ5H wrote:
Just the Hustler base, the entire bugcatcher coil and a 103 " whip.
I expected it to be lower in impedance at resonance.

What bugcatcher coil was it? Obviously not the big one. Is the
Hustler base the one that hinges? If so, it might not be
conducting properly.
--
73, Cecil http://www.qsl.net/w5dxp



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Yes it is the "big one" but I suspect that, since I cobbled it together,
that R is a big issue.
I don't care since it isn't a realistic solution. I used it "parked mobile"
in 1970.
Comparing the Nott with the Tarheel should be fun.
H.
NQ5H


"Cecil Moore" wrote in message
...
H. Adam Stevens, NQ5H wrote:
Just the Hustler base, the entire bugcatcher coil and a 103 " whip.
I expected it to be lower in impedance at resonance.

What bugcatcher coil was it? Obviously not the big one. Is the
Hustler base the one that hinges? If so, it might not be
conducting properly.
--
73, Cecil http://www.qsl.net/w5dxp



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H.,
When you find out that the aluminum/copper base
makes no difference at all, can I have the one you
don't want?
'Doc

"Cecil Moore" wrote in message
...
H. Adam Stevens, NQ5H wrote:
Just the Hustler base, the entire bugcatcher coil and a 103 " whip.
I expected it to be lower in impedance at resonance.

What bugcatcher coil was it? Obviously not the big one. Is the
Hustler base the one that hinges? If so, it might not be
conducting properly.
--
73, Cecil http://www.qsl.net/w5dxp


Yes it's the big one; I suspect dirt in the threads.
It's an impractal monster anyway.
73
H.